I have built constant current source using ua741 amplifier and npn BJT bc639. Circuit gives constant current of 100mA. My new problem is how to control that output current from let say from 20 to 100mA by output voltage. The whole project goes like this; the circuit has to give constant current (max. 100mA) which amount has to be regulated from outside with voltage.

You can attach it to your first post by using the Edit button, and then click the Go Advanced button below the text box. On the next screen, click the Manage Attachments button, navigate to your image on your computer, select it, and then click the Upload button.

The load is changing between 0.5 and 2kΩ. the basic scheme and file for multisim simulator is in attachment.the current through load is constant and the problem is to control the amount of that current (max 100mA) with voltage.i think that should be an another circuit that control current trough the load.

i have no idea how to build that and mentor will not help me he said the task is:constant current source max 100mA the load variate between 0.5 and 2kΩ the amount of that current must be regulated by voltage 0 to 1V from another source, something like input signat to the circuit.

WOW that was impressive..hehe
well, could u plz tell me what if i feed the input with 12V whereby the gain is -10 so isn't it irrational to get an output of -120Volts...?????
i could have been killed in the lab if it was so.!!!!!